<?php

namespace PHPExcel\Shared\Trend;

/**
 * PHPExcel_\PHPExcel\Shared\Trend\Trend
 *
 * Copyright (c) 2006 - 2015 PHPExcel
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 *
 * @category PHPExcel
 * @package PHPExcel_Shared_Trend
 * @copyright Copyright (c) 2006 - 2015 PHPExcel (http://www.codeplex.com/PHPExcel)
 * @license http://www.gnu.org/licenses/old-licenses/lgpl-2.1.txt LGPL
 * @version ##VERSION##, ##DATE##
 */
class Trend {
    const TREND_LINEAR = 'Linear';
    const TREND_LOGARITHMIC = 'Logarithmic';
    const TREND_EXPONENTIAL = 'Exponential';
    const TREND_POWER = 'Power';
    const TREND_POLYNOMIAL_2 = 'Polynomial_2';
    const TREND_POLYNOMIAL_3 = 'Polynomial_3';
    const TREND_POLYNOMIAL_4 = 'Polynomial_4';
    const TREND_POLYNOMIAL_5 = 'Polynomial_5';
    const TREND_POLYNOMIAL_6 = 'Polynomial_6';
    const TREND_BEST_FIT = 'Bestfit';
    const TREND_BEST_FIT_NO_POLY = 'Bestfit_no_Polynomials';
    
    /**
     * Names of the best-fit Trend analysis methods
     *
     * @var string[]
     *
     */
    private static $trendTypes = array(
    self::TREND_LINEAR,
    self::TREND_LOGARITHMIC,
    self::TREND_EXPONENTIAL,
    self::TREND_POWER 
    );
    
    /**
     * Names of the best-fit Trend polynomial orders
     *
     * @var string[]
     *
     */
    private static $trendTypePolynomialOrders = array(
    self::TREND_POLYNOMIAL_2,
    self::TREND_POLYNOMIAL_3,
    self::TREND_POLYNOMIAL_4,
    self::TREND_POLYNOMIAL_5,
    self::TREND_POLYNOMIAL_6 
    );
    
    /**
     * Cached results for each method when trying to identify which provides the best fit
     *
     * @var bestFit[]
     *
     */
    private static $trendCache = array();
    public static function calculate($trendType = self::TREND_BEST_FIT, $yValues = array(), $xValues = array(), $const = true) {
        // Calculate number of points in each dataset
        $nY = count($yValues);
        $nX = count($xValues);
        
        // Define X Values if necessary
        if ($nX == 0) {
            $xValues = range(1, $nY);
            $nX = $nY;
        } elseif ($nY != $nX) {
            // Ensure both arrays of points are the same size
            trigger_error("Trend(): Number of elements in coordinate arrays do not match.", E_USER_ERROR);
        }
        
        $key = md5($trendType . $const . serialize($yValues) . serialize($xValues));
        // Determine which Trend method has been requested
        switch ($trendType) {
            // Instantiate and return the class for the requested Trend method
            case self::TREND_LINEAR :
            case self::TREND_LOGARITHMIC :
            case self::TREND_EXPONENTIAL :
            case self::TREND_POWER :
                if (!isset(self::$trendCache[$key])) {
                    $className = '\PHPExcel\Shared\Trend\\' . $trendType . 'BestFit';
                    self::$trendCache[$key] = new $className($yValues, $xValues, $const);
                }
                return self::$trendCache[$key];
            case self::TREND_POLYNOMIAL_2 :
            case self::TREND_POLYNOMIAL_3 :
            case self::TREND_POLYNOMIAL_4 :
            case self::TREND_POLYNOMIAL_5 :
            case self::TREND_POLYNOMIAL_6 :
                if (!isset(self::$trendCache[$key])) {
                    $order = substr($trendType, -1);
                    self::$trendCache[$key] = new PolynomialBestFit($order, $yValues, $xValues, $const);
                }
                return self::$trendCache[$key];
            case self::TREND_BEST_FIT :
            case self::TREND_BEST_FIT_NO_POLY :
                // If the request is to determine the best fit regression, then we test each Trend line in turn
                // Start by generating an instance of each available Trend method
                foreach ( self::$trendTypes as $trendMethod ) {
                    $className = '\PHPExcel\Shared\Trend\\' . $trendType . 'BestFit';
                    $bestFit[$trendMethod] = new $className($yValues, $xValues, $const);
                    $bestFitValue[$trendMethod] = $bestFit[$trendMethod]->getGoodnessOfFit();
                }
                if ($trendType != self::TREND_BEST_FIT_NO_POLY) {
                    foreach ( self::$trendTypePolynomialOrders as $trendMethod ) {
                        $order = substr($trendMethod, -1);
                        $bestFit[$trendMethod] = new PolynomialBestFit($order, $yValues, $xValues, $const);
                        if ($bestFit[$trendMethod]->getError()) {
                            unset($bestFit[$trendMethod]);
                        } else {
                            $bestFitValue[$trendMethod] = $bestFit[$trendMethod]->getGoodnessOfFit();
                        }
                    }
                }
                // Determine which of our Trend lines is the best fit, and then we return the instance of that Trend class
                arsort($bestFitValue);
                $bestFitType = key($bestFitValue);
                return $bestFit[$bestFitType];
            default :
                return false;
        }
    }
}
